The present invention relates generally to an in-line swivel for use in drilling and pipeline operations. More particularly, the invention relates to an in-line swivel permitting deflection when the tubular string below the swivel is deflected by relative motion from the longitudinal axis of the remainder of the tubular string. More particularly still, the invention relates to an in-line swivel permitting deflection of a pipe string resulting from “wave action” and wind changes experienced when used in conjunction with floating drilling rigs or tankers.
The use of in-line drill string swivels in drilling applications has long been known to those in the drilling industry. Often, during sea-based drilling operations on floating platforms, the drill string suspended from a drilling mast may experience movement not generally experienced by land based drilling rigs which are fixed to the ground. These floating drill rigs may have drilling masts extending hundreds of feet above the rotary table support the drill string hanging below. If the rotary table floor rotates or rocks while the in-line swivel is supporting the drill string, damage may occur to the drill string or Kelly drive. Particularly, if a drill string on a movable platform is connected to a fixed or rigid tubular string, stress and strain will build up if a provision to allow rotation and deflection therebetween is not present. Furthermore, movement of the platform or vessel from wave action or wind (or intentional movements) can overstress and even loosen a threadably connected pipe string. Finally, in addition to “drill string” applications, other applications of pipe, either threadably connected or bolted, exist where angular and rotational deflections are an issue.